[llvm-dev] funnel shift, select, and poison

John Regehr via llvm-dev llvm-dev at lists.llvm.org
Mon Feb 25 12:06:52 PST 2019

>> It is definitely unsound to assume call(poison) == poison, because not 
>> every function returns a value that is poison-dependent on the 
>> function's arguments.
> That's exactly the same as for a "select".

But that is not what the LangRef says. It says that for purposes of 
poison: "Values other than phi nodes depend on their operands."

Most people, I think, would agree that select should not poison-depend 
on its not-selected operand. This is one of the things that needs to be 


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